Nevil Maskelyne - father of Greenwich Mean Time
The Rev Dr Nevil Maskelyne was the fifth British Astronomer Royal and led the first person quest to scientifically measure the mass of the planet Earth. He was also involved in the famous search for an accurate way to measure longitude at sea, alongside John Harrison, and his work led to the establishment of the concept of Greenwich Mean Time.
Maskelyne was born in London in 1732 and became interested in astronomy whilst at Westminster School. He became a clergyman, but also a Fellow of the Royal Society, who sent him in 1760 to observe the transit of Venus from the island of St. Helena in the South Atlantic. The weather was poor, but the trip wasn't completely wasted as Maskelyne took the opportunity to trial a method of determining longitude using the position of the moon. Upon his return, he published tables that could be used by navigators at sea.
Whilst determining latitude whilst at sea was reasonably easy using the angle of the sun at noon, determining a ship's longitude was much trickier and led to many lost vessels and a good number of shipwrecks.
In 1763 the Board of Longitude, a government body seeking a solution to this problem, sent Maskelyne to Barbados to carry out an official trial of three contenders for the prize money they were offering. This competition was eventually won by the clock-maker John Harrison.
In 1765 Maskelyne was appointed Astronomer Royal. His method of calculating longitude according to the position of the moon continued to used, alongside Harrison's marvellous (but extremely expensive) clocks. Maskelyne's tables were produced annually and became the Nautical Almanac. Since these were so widely used, and Maskelyne made his lunar observations from the Royal Observatory, Greenwich - Greenwich was adopted as the international Prime Meridian in 1884, though Maskelyne himself had died much earlier in 1811.
In 1772, as Astronomer Royal, Maskelyne suggested that an experiment to calculate the mass of planet Earth would "do honour to the nation where it was made" and proposed mountain sites in the UK to test the concept. It was decided that the best candidate was Schiehallion, a peak in the central Scottish Highlands, which stood in isolation from any nearby hills, so making the calculations more straightforward.
Maskelyne, Charles Hutton and Reuben Burrow performed the experiment. Completed by 1776, it was calculated that the mean density of the Earth must be greater than that of normal rock, suggesting for the first time that the interior of the Earth might be substantially composed of metal.
Further reading
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